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Maximum Lift - Clearance

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Matthew68
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Maximum Lift - Clearance

Post #1 by Matthew68 » Sun May 19, 2019 11:05 pm

Hi All,

For those who chimed in on my DCR thread - thanks! I settled on the 270/270 110 cam from Schneider and talking to Jerry about my build. In the cam specs (custom grind), he stayed the valve lift would be .485” with my YT 1.65 roller rockers. I recall a post by X (I think) that anything over .490” would have piston to valve clearance issues. Do I need to re-evaluate my cam choice? I haven’t purchased it yet. My motor specs below, based on these am I running a high risk of piston/valve interference? Note that this is all planned machine work - haven’t had it done yet so I can course correct if recommended.

1968 200ci block - bore TBD (20 or 30 over)
Planned zero deck
Flat top pistons (I haven’t found any with reliefs)
Planned 10:1 static compression ratio
Aluminum head/intake with 1.84” intake valves
53cc combustion chamber size
Victor head gasket (.044” thickness compressed)

I realize my questions are all theoretical and must be measured which I plan to do upon assembly. However, I don’t want to be in a situation where I’m dangerously close and it’s too late to leave a little meat on the deck, change to a felpro gasket, etc to give me more room.

Thoughts? Appreciate any advice.

Cheers,
Matthew
1968 Mustang Coupe 200ci - Pertronix + Coil
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rbohm
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Re: Maximum Lift - Clearance

Post #2 by rbohm » Sun May 19, 2019 11:48 pm

mathew, as you have already noted, any combination you come up with will have to be checked before final assembly. this is why mock up is so important.

so start by finding out what your current v/p clearance is. you will also need the current compressed gasket thickness, and the depth the piston is down in the cylinder.

now install the cam you are going to use and get the v/p clearance for that combination. now you can play with the numbers and figure out how much you need to clearance the pistons before you rebuild the short block. it owuld be a good idea to build the head like you want it before checking the v/p clearance so you can use it to figure what you need to do to the new pistons.
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chad
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piston/valve Clearance

Post #3 by chad » Mon May 20, 2019 12:59 am

must B some way to strategise here...
no paper method? Charts, tables, formula?
Didn't I C a guy on here shave a piston top on
(I think it wuz) a Bridgeport a yr ago/or wuz it
2? Least the table looked like one. Now let's see

1/2 the small end + the C-rod + to the piston pin C/L +
the squish...
:hmmm:
:P
:shock:
:oops:
Last edited by chad on Mon May 20, 2019 8:40 am, edited 1 time in total.
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), 250, NV 3550 & DSII to B transplanted, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. chrlsful@aol.com (413) 259-1749

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Re: Maximum Lift - Clearance

Post #4 by xctasy » Mon May 20, 2019 2:21 am

Its based on overlap, not lift.


See
http://vb.foureyedpride.com/showthread. ... -clearance

for how to do it on a 302

Ak Miller noted that on a 260 to 290 at lash cam, 490 thou on a zero decked block with a mild head plane could get you into problems.

Specific issue is the last post by Jeff Cooke on a 302 engine with flat tops. The wedge head 200 has similar issues at high lifts and intake and exhaust durations.

http://vb.foureyedpride.com/showthread. ... e-question
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Re: Maximum Lift - Clearance

Post #5 by Matthew68 » Mon May 20, 2019 10:32 am

rbohm wrote:mathew, as you have already noted, any combination you come up with will have to be checked before final assembly. this is why mock up is so important.

so start by finding out what your current v/p clearance is. you will also need the current compressed gasket thickness, and the depth the piston is down in the cylinder.

now install the cam you are going to use and get the v/p clearance for that combination. now you can play with the numbers and figure out how much you need to clearance the pistons before you rebuild the short block. it owuld be a good idea to build the head like you want it before checking the v/p clearance so you can use it to figure what you need to do to the new pistons.


Thanks, but my setup I took apart was a stock 68 head and block. That head has long been since removed and had the stock cam and stock 6.5cc dished pistons. I’ll be using the aluminum cylinder head for the first time and I’ll be dropping the block off for all machine work. They’ll also disassemble and assemble. I suppose I could take the head and have them measure, or I could wait until. Have the head here and do it before drop off. The only thing is I’m planning to not use the dished pistons to gain some compression so I’m not sure what my best course of action is here.
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Re: Maximum Lift - Clearance

Post #6 by CZLN6 » Mon May 20, 2019 11:28 am

Howdy Matt and All:

My first thought is why not hold off on the 1.65 rocker arms and start with 1.5. You can alway add higher lift rocker arms later- if you think you still need more lift. You didn't say what the lift at the cam is? The extra lift from the 1.65 compared to 1.5 isn't much, but it may minimize clearance issues. Just a thought.

Adios, David
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Re: Maximum Lift - Clearance

Post #7 by Matthew68 » Mon May 20, 2019 2:28 pm

CZLN6 wrote:Howdy Matt and All:

My first thought is why not hold off on the 1.65 rocker arms and start with 1.5. You can alway add higher lift rocker arms later- if you think you still need more lift. You didn't say what the lift at the cam is? The extra lift from the 1.65 compared to 1.5 isn't much, but it may minimize clearance issues. Just a thought.

Adios, David


Hi David,

Here are the cam specs:

270-H
270 DURATION
214 @ .050"
.485" LIFT WITH 1.65 ROCKER
110 LOBE CENTER
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Re: Maximum Lift - Clearance

Post #8 by pmuller9 » Mon May 20, 2019 4:22 pm

There will not be a valve to piston clearance issue.
The intake valve sits at least .250" in the chamber.

If you do the math, if you advance the 270H cam 3 degrees the intake lobe center will be at 107* ATDC which puts the .050" lobe lift right at TDC.
.050" lobe lift times the 1.65 ratio rocker opens the intake valve .082" at TDC.
The tightest point between intake valve to piston occurs between 10 and 15 degrees ATDC.
That particular cam lobe has a lobe lift of .100" at that point which puts the valve lift at .165" but the piston is now .038" down in the hole for a difference of .127"
The piston is now .045" closer to the valve but there is still plenty of clearance.

Now add the .044" thick head gasket for additional clearance.

Do the check once you get the cam and head to verify.

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Re: Maximum Lift - Clearance

Post #9 by drag-200stang » Mon May 20, 2019 6:36 pm

I also agree with Mr. Muller, you will not have a piston to valve issue...But always verify.
The biggest issue on these engines is the short valves, that is where high lift can start to be a problem at about .500 ...The bottom of the retainer can contact the seal and guide...Easy to measure with the spring off...I do not think that you will have a problem, but verify.
Another thing to watch for is spring coil bind....I am sure that your cam guy gave you springs that will work, but verify on your head .
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Re: Maximum Lift - Clearance

Post #10 by wsa111 » Mon May 20, 2019 8:30 pm

CZLN6 wrote:Howdy Matt and All:

My first thought is why not hold off on the 1.65 rocker arms and start with 1.5. You can alway add higher lift rocker arms later- if you think you still need more lift. You didn't say what the lift at the cam is? The extra lift from the 1.65 compared to 1.5 isn't much, but it may minimize clearance issues. Just a thought.

Adios, David
Cannot do this the 1.65 Yella-terra rockers require V-8 oil through lifters & pushrods The oil galley on the LR of the of the block has to be blocked to prevent an oil leak.
You will have no clearance problems.
If you really want to be sure put a ball of clay on the piston top & turn the engine over.
Don't worry you are good to go.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, DSII dist. MSD-6al & MSD-Blaster 8252 Coil. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
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p/v clearance, springs, oiling - any more?

Post #11 by chad » Mon May 20, 2019 10:22 pm

"...require V-8 oil through lifters & pushrods The oil galley on the LR of the of the block has to be blocked to prevent an oil leak...."
even on the alu head Bill? I think that's in use here~
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), 250, NV 3550 & DSII to B transplanted, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. chrlsful@aol.com (413) 259-1749

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Re: p/v clearance, springs, oiling - any more?

Post #12 by Matthew68 » Tue May 21, 2019 6:30 am

chad wrote:"...require V-8 oil through lifters & pushrods The oil galley on the LR of the of the block has to be blocked to prevent an oil leak...."
even on the alu head Bill? I think that's in use here~


It’s for the Yella Terra rockers
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